The present invention relates to semiconductor power conversion apparatuses using semiconductor elements and, more particularly, to a semiconductor power conversion apparatus which suppresses an overvoltage upon switching operation.
In such a semiconductor power conversion apparatus having a MOS (Metal Oxide Semiconductor) gate semiconductor, such as an IGBT (Insulated Gate Bipolar Transistor) power conversion apparatus, an IGBT element (device) is switched to achieve AC/DC power conversion, DC voltage conversion, AC voltage/frequency conversion, etc. However, when the IGBT is turned OFF, an energy, accumulated in the parasitic inductance of a wiring line when a current flows therethrough, causes a surge voltage to be applied to the IGBT. A method of preventing the destruction of the IGBT element caused by the surge voltage induced upon the turning off of the IGBT, that is, by the overvoltage applied to the IGBT, is disclosed, for example, in JP-A-11-17831. In the prior art, a series circuit of a clamping element and a resistor is provided between a collector of the IGBT and a gate thereof, so that the voltage of the IGBT exceeding the voltage of the clamping element causes a charging current to be supplied from the clamping element to the gate of the IGBT. And setting of a higher gate voltage for the IGBT causes the impedance of the IGBT to be reduced, thus protecting the IGBT from an overvoltage. In the prior art, further, such a means is disclosed as to provide a plurality of series circuits each having the clamping element and the resistor and to set different voltages for the respective clamping elements, thus supplying more charging current for a higher collector voltage. In general, even when a gate charging current is supplied from a clamping element, the current is shunted to a gate driver and thus it is impossible to secure a sufficient amount of the gate charging current. However, since the higher collector voltage can supply more charging current in the prior art, we can say that the prior art is excellent from the viewpoint of reliably protecting the IGBT from the overvoltage upon application thereof.